Railway-traffic-controlling apparatus



March 5, 1929. c. s. SNAVELY RAILWAY TRAFFIC CONTROLLING APPARATUS FiledMay 29. 1926 Patented Mar. 5, 1929.

UNITED STATES CLARENCE S. SNAVELY, OF PITTSBURGH,

SWITCH & SIGNAL COMPANY, OF SWI OF II?ENN'SYLVANIA. V

PENNSYLVANIA, ASSIGNOR TO THE UNION SSVALE, PENNSYLVANIA, A CORPORATIONRAILWAY-TR.AFFIC-CONTROLLING APPARATUS. 7

Application filed May 29, 1926. Serial- No. 112,491.

My invention relates to railway traffic controlling apparatus, andparticularly to apparatus of the type comprising train carried governingmeans controlled by energy received from the trackway.

One object of my present invention is the provision, in apparatus of thetype described, of means for supplying the trackway with alternatingcurrents periodically interrupted at different frequencies, andgoverning means on the train selectively responsive to the frequency ofinterruption of such currents. 1 v

I will describe one form of railway traflic controlling apparatusembodying my invention, and will then point out the novel featuresthereof in claims.

The accompanying drawing is a'diagrammatic view showing one form ofrailway traffic controlling apparatus embodying my invention.

Referring to the drawing, the reference characters 1 and 1 designate thetrack rails of a stretch of railway track over which traffic normallymoves in the direction indicated by the arrow. These track rails aredivided, by means of insulated joints 2, into a plurality ofsuccessivetrack sectionsA.B,-BC,et c. Each track section is providedwith a track transformer designated by the reference character T with anexponent corresponding to the location and having a secondary constantlyconnected with the rails adjacent the exit end of the section throughthe usual impedance 6. Each track section is further provided with apolarized track relay designated by the reference character R with asuitable distinguishing v exponent and comprising two windings 8 and 9.One winding 8 of each track relay is constantly connected across therails adjacent the entrance end of the associated section. The remainingwinding 9 of each track relay is constantly supplied with alternatingcurrent from secondary 10 of an adjacent line transformer designated bythe reference character J with an appropriate exponent and having itsprimary 11 constantly supplied with alternating current from a suitablesource such as an alternator N over line wires 3 and 3. The track relaysB may be used to control. governing 'means, not shown 1n the drawmg,

in any suitable manner.

' Associated with each track relay is a repeater relay designated bythereference character P with an exponent corresponding to the location andarranged 'to be energized only when the associated track relay isencrgized in'one direction or the other. Referring particularly to relayP, the circuit for this relay may be traced from secondary 10 oftransformer J through wires 19, and 21, contact 22 of relay B in thenormal or reverse positions, wire 23, winding of relay P and wires 24,25, 26, 27 and 28 back to secondary 10 of transformer J r 1 Each tracksection is also provided with a coding relay designated by the referencecharacter S with an appropriate exponent. Each coding relay S comprisestwo windings X and Y, each made up oftwo coils 14 and 15, and a pivotedarmature controlled by the yvindings. The armature 16' controls twocontacts 17 and 18, which. are arranged to occupy one extreme positionor the other according as armature 16 is attracted by Winding X orwinding Y. Associated with each relay S is a rectifier designated by thereference character Q, with a suitable exponent. Referring particularlyto relay S when relay P is energized a circuit is closed from secondary10 .of transformer J through wires 19, 29 and 29 rectifier (2?, wires 30and'30, front contact 31 of relay P wire 32, coil 14 of winding Y andcoil 14 of winding X, wire 33, frontcontact 34 of relay P wires 35 and36, rectifier Q and Wires 71, 27 and 28, back to secondary 10 oftransformer J It will be seen thatby Virtue of this circuit, the coils14 of windings X and Y are supplied from transformer J B with directcurrent which flows through the coils in series. Coil 14 of winding X isprovided with a shunting circuit which may be traced from the lowerterminal of this coil, through wire33, front contact 34 of relay P wires35 and 38, back contact 39 of rela R wire 40, and contact 17-1'7 ofrelay B to the upper terminal of coil 14 of winding X. When contact1717" is closed coil 14 of winding Y is shunted through a circuit whichmay be traced from the lower terminal of coil 14 of winding Y, throughwire 32,. front contact 31 of relay P wires 30 and 41, and contact17-1'1" of relay S back to the upper terminal of coil 14 of winding Y.As 'shownin, the drawing armature 16 is swung toward winding X but relayR is energized, so that the shunting circuit for coil 14 of winding X isopen. The

shunting circuit for coil 14 of winding Y is also open at contact 17-17,but armature 16 is held by winding X in such position that contact 1717is closed because of the re duced air gap between armature 16 andwinding X, though current is supplied to coils- 14 of windings X and Yin series. Should relay R become deenergized, the shunting circuit forcoil 14 of winding X would he closed. The magnetic field due to thiscoil would then gradually decay until the comparatively large attractionof coil 14 of winding Y would swing armature 16 toward winding Y. Thisreversal of the armature would open the shunt for coil 14 of winding Xand would close the shunt around coil 14 of winding Y. After a timeinterval the increasing field of coil 14 of winding X would predominateover the decreasing field of coil 14 of winding Y and armature 16 wouldbe swung back into the position in which it is illustrated in thedrawing. It follows that when relay R is deenergized, relay S operatesto close contact 18,1S and contact l818" intermittently.-

' WVhen relay P is de-energized the oper ating circuit for relay S maybe traced from secondary 10 of transformer J, through wires 19, 29, and29, rectifier Q), wires 30 and 30, back contact 31 of relay 1 wire 37,coils l5 and 14 of winding Y, coils l4 and 15 of winding X in series,wire 70, back contact 34 of relay P, wires 35 and 36, rectifier Q, andwires 71, 27 and 28 back to secondary 10 of transformer J If relay R isde-energized when relay P is de-energized, a shunting circuit forwinding X is closed each time contact 1'717 of relay S closes. Thisshunting circuit passes from the lower terminal of this winding throughwire 70, back contact 34 of relay P wires 35 and 38, back contact 39 ofrelay R wire 40, contact l717""of relay S and back to the upper terminalof winding X. Similarly a shunting path of low resistance is closedaround winding Y when contact 1717 of relay S is closed from the lowerterminal of winding Y, through wire 37, back contact 31 of relay P wires30 and 41, contact 1717"-of relay S and back to the upper terminal of'winding Y. It follows therefore that when relay P is de-energized andrelay R is also tie-energized the operation of relay S alternatelycloses contact 1818 and contact 1818 It should he pointed out that whenrelay P is energized only coils 14 of windings X and Y are included inthe operating circuit for relay S, but that when relay if isde-energized, both coils of windings X and Y are included in theoperating circuit. Due

to the increased reactance ofthe windings 'X and Y when both coils areincluded in the circuit, the operation of the relay is more rapid whenonly one 0011 of the winding is included in the operating circuit thanwhen both coils are included in the circuit. The relays S may bearranged to operate at any reasonable speeds but for purposes ofillustration I will assume that when relay P is energized relay Soperates at 100 cycles per minute and that when relay P is de-energized,relay 8 operates at 30 cycles per min ute. It 'will he noted that whenrelay S is operated at either speed, if back contact 39 of relay Rbecomes open the shunt around that portion of winding X which is thenincluded in the operating circuit is opened and when the armature 16next swings toward winding X, the operation of the relay ceases and thearmature remains in that position until back contact 39 of relay R isagain closed.

\Vhen relay R is energized in one direction or the other, so that relayS is at rest, contact 18l8" of relay S is closed and current-is suppliedwithout interruption to the primary 7 of transformer T from secondary 10of transformer J B in the manner I will now describe. If relay P isenergized, current is supplied from secondary 10 of transformer J,through wires 19 and 29, contact 18-18 of relay S wires 56'and 57,contact 58 of relay R wire 59, front contact 60 of relay 1 wire 61,primary 7 of transformer T", wire 62, front contact 63 of relay P, andwires 64, 26, 27 and 28, back to secondary '10 of transformer J. Thiscircuit is closed only when relays P and B" are energized and whencontact 1818 of relay SP is closed, under which condition currentofnormal rela tive polarity is supplied to the rails of SLL tion AB,thereby swinging contacts 22, 5b and 39 of relay R to the right. Whenrelay P is dc-energized, however, current from sec ondary 10 oftransformer J flows through wires 19 and 29, contact 1818 of relay s",wires 56 and 65, back contact 63 of relay P wire 62, primary 7 oftransformer T, wire 61, back contact 60 of relay P and wires 64, 26, 27and 28 back to secondary 10 of trans former J. When this circuit isclosed current of reverse relative polarity is supplied to the rails ofsection AB and relay R is energized in the reverse direction so that thecontacts of this relay are swung to the left.

Means are also provided for at times supplying each track section withinterrupted alternating train controlling current. The immediate sourceof this train controlling current for each track section is atransformer designated by the reference character K with an exponentcorresponding to thelocation and having a primary 13 constantly suppliedwith alternating current from a suitable source such as an alternator Mover line wires and 4. The frequency of the current supplied byalternator N is different from that. supplied by alternator and sincecurrent fromaltcrnat-or N is supplied to the trackway for energizing thetrack relays these relays are constructed to respond only to cur-- K byalternator M is of 100 cycles per second butthese particular frequenciesare not essential and have been mentioned simply-for purposes ofillustration.

Train controlling current is supplied to the rails of a section onlywhen the coding relay S for that section is operating. Forlay S is atrest and the track circuit current example, when relay 1? is energizedand when relay R is de-energized to operate relay S at 100 cycles perminute, an impulse of train controlling current is supplied to primary 7of transformer T for each cycle of operation of relay S the circuitbeing traced from secondary 12 of transformer K through wire 42, contact18-18" of relay S wires 56 and 57, contact 58 of relay R wire 59, frontcontact 60 of relay P Wire 61, primary 7 of transformer T wire 62, frontcontact 63 of relay P and wires 64, 26,27 and 43, back to secondary 12of transformer K When relays R and P are energized, then, and when relayS is operating, the rails of the section AB are'supplied with an impulseof train controlling current each time contact 1818 of relay S isclosed, and with an impulse of track circuit current each time contact18-18'- is closed. lit follows that the rails of the section are thensupplied with, alternate impulses of train controlling current and trackcircuit current, the frequency of the-impulses of each current being 100cycles per minute. Train controlling current supplied to the rails atthis frequency of interruption I shall term the proceed code. When relayP is-deenergized and when relay S is operating, an impulse of traincontrolling current is supplied as before to the trackway each time contact 1818 is closed, the circuit for transformer T then passing fromsecondary 12 of transformer K through wire 42, contact 18--18 of relay Swires 56. and 65, back contact 63 of relay P wire 62, primary 7 oftransformer T wire 61, back contact 60 of p relay P 'and wires 64, 26,27 and 43 back to the section in the form of impulses having a secondary12 of transformer K When this circuit is closed and when relay R isdeenergized relay S operates at 30 cycles per minute,.and the rails ofsection A'B are supplied with alternate impulses of train controllingcurrent .and of track circuit current, the'frequency of interruption ofeach current being 30 cycles per-minute. Train controlling currentsupplied to the rails of frequency of 30 cycles per minute, I shall termthe caution code.

As shown in the drawingthe section to the right of point C is occupiedby a train-indicated diagrammatically at V. Relay R is thereforede-energized and relay P is also deenergized. Trackcircuit current ofreverse relative polarity is therefore supplied to the rails of sectionB-G. Relay B is therefore energized in the reverse directionvso thatrelay S is at rest arid the track' circuit current supplied to sectionBC is uninterrupted.

No train controlling current is supplied to the rails of section BG.Relay P is energized and track circuit current of normal relativepolarity is therefore supplied to the rails of section AB. Relay Rtistherefore energized .in the normal direction so that resuppliedftosection 'A- B is uninterrupted. In similar manner relayP is energized,but the section to the left of point A is occupied by a second train V,so that the track relay for this section is de-energized and relay S isoperating at 100 cycles per minute. The

rails of the section to the left of point A are therefore supplied withtrain controlling current in the form of a proceed code, and during theinterval between successive impulses of such train controlling current,

track circuit current of normal relative polarityis supplied to therails of the section.

Carried upon the train V in advance'of the forward axleis a receiver Wcomprising two magnetizable cores 66 and 66" located in inductiverelation with the track rails 1 and 1 respectively. Core 66 is providedwith a winding 67, and core 66*- is provided with a similar winding 67the two windings 67 and 67 being connected in series in such manner thatthe voltages induced therein by train" controlling currents flowing inopposite directions in the two track rails at an instant are additive.The windings 67 and 67 of the receiver W are connected, through anamplifier 68 and a rectifier 69 with a relay D. By

means of a condenser 80, the windings 67 and 67 arev tuned to resonanceat the frequency of the train controlling current so that the relay D isenergized by train controlling current but not by 60 cycle track circuitcurrent in the track rails. It follows that relay D is intermittentlyenergized when the rails 0ccupied by the train V are supplied with traincontrolling current, the frequency of energization of relay 1)corresponding to the frequency of interruption of such train controllingcurrent.

' The reference characters G and Gr designate two" transformers eachcomprising a magnetizable core 44 and a secondary 47. When relay Disintermittently energized, periodically varying fluxes of a frequencycorresponding to the frequency of energization of relay D are createdinthe cores of transformers G and G As here shown this is D isenergized, :direct current is supplied from a suitable source such as abattery F, to primaries 45 of transformers G and Gr in parallel. Whenrelay D is de-energized, however, direct current flows through primaries46 of these transformers in parallel from battery F. It will be notedthat current flows in opposite directions through the two primaries ofeach transformer and it follows that when relay D is being energizedintermittently by the interrupted train controlling current, themagnetic fluxes in transformers G and G are periodically reversed at afrequency corresponding to the frequency of interruption of the traincontrolling current received by relay D. Secondary 47 of transformer Gis connected, through a rectifier L with a direct current relay E .Therectifier L may be of any suitable type and as here shown comprisesfourasymmetrical units 48 so arranged that current in relay E alwaysflows in a direction from the righthand terminal to the left-handterminal of the relay. The variations in the flux in the core oftransformer G create surges of current in relay E and to assist therelay in holding closed its front contact during successive surges Iconnect an asymmetrical unit 49 in parallel with the relay E. This unit49 is arranged to offer a high resistance to current supplied fromrectifier L but to offer a low resistance to current resulting from thedecaying field of the relay winding during the interval of time betweensuccessive impulses supplied to the relay. The snubbing effect of theunit 49 therefore renders relay E slow releasing but does not interferewith the quick pick-up of the relay. It should also be pointed out thatthe asymmetrical units of rectifier L assist in this snubbing effect,the units 48 comprising two parallel paths each containing two of theunits'in series and conducting current in the same direction as unit 49during the decay of the field of relay El.

In similar manner a second relay E is connected with secondary 47 oftransformer G through a rectifier L and is provided with an asymmetricalunit 49 connected in parallel therewith.

It is well known that if a transformer is designed so that for an inputelectromotive force of one amplitude and frequency the core issubstantially saturated, a certain amount of energy will be delivered atthat frequency and atleast as much energy will be delivered at higherfrequencies, but that at lower frequencies with the same amplitude ofelectromotive force a smaller amount of energy is delivered by thetransformer. I take advantage of this principle to select between thecaution and proceed codes on board the train.

This is accomplished by so proportioning the parts that when the flux intransformer G is being reversed 30 times per minute, as

when relay D is receiving the caution code, the

core of the transformer-is substantially saturated and relay E issupplied with suflicient energy to pick up the relay. It follows thatrelay E will also be energized when the flux is being reversed 100 timesper minute, as when relay D is receiving the proceed code. Transformer Gis so proportioned that when the flux is being reversed 100 times perminute, its core is substantially saturated and sufficient energy issupplied to relay E to pick up the relay.- When the caution code isbeing received, however, relay E is de-energized, because the reversalsof flux are of the same amplitude .as for the proceed code, due to thesaturation of the core, and since theyare less rapid the energy suppliedto the relay E is not sufficient to energize the relay.

I will now assume that the train V proceeds through the stretch of trackshown in the drawing. While the train is in the section to the left ofpoint A, the proceed code supplied to the rails of this sectionenergizes relay D intermittently at the rate of 100 cycles, per minute.Relays E and L are therefore both energized so that current flows frombattery F, through front contact 5151" of relay E to lamp 53, lightingthis lamp to indicate proceed. As the train enters sec-Zion. AB, thede-energization of relay R sets relay S into operation. Relay P isenergizedand relay S therefore operates at 100 cycles per minute. Therails are therefore supplied with train controlling current inaccordance with the proceed code so that as the train proceeds throughsection A-B .relays E and E .remain in their energized conditions andlamp 53 remains lighted to indicate proceed. As the train enters sectionBC, relay R becomes de-energized and sets relay S into operation. RelayP is de-energized, however, so that relay S operates at 30 cycles perminute. Train controlling current is there fore supplied to the rails ofsection BC in accordance with the caution code. Relay D is thereforeenergized intermittently 30 times each minute.v Asa result the fluxes intransformers G and G are reversed 30 times each minute. The energy thussupplied to relay E is not sufiicient to hold this relay inv itsenergized condition so that this relay opens but relay E is held in itsenergized condition. Current then flows from battery F, over backcontact 5151 of relay E and front contact 52-52 of relay E to lamp 54,energizing this lamp to indicate caution. Should the train enter thesection to the right of point C, relay D would be deprived of traincontrolling cur.- rent and would be continuously de-energized so thatrelays E and E would both be deenergized and current from battery Fwould flow to lamp 55 over back contact 51-51 of relay E? and backcontact 52.52 of relay E Lamp 55 would then be lighted to indicate stop.a

When the train passes out of section AB, the next impulse of trackcircuit current enerquency,

gizes relay R and opens the shunt around the portion of winding X thenincluded in the operating circuit for relay 8, thereby causing theoperation of this relay to cease, and discontinuing the interruption inthe track circuit current supplied to the section. At the same time thestopping of relay S completely interrupts the supply of traincontrolling current to the rails of the section. In similar manner whena train leaves any of the remaining sections the operation of the codingrelay for that section immediately ceases and uninterrupted trackcircuit current is thereafter supplied to the rails of the section aslong as the section is unoccupied.

In this application I have shown the coding relays S provided with onlytwo coils in each winding to give two speeds for the relay, and thetrain carriedapparatus is arranged to select between only twofrequencies of the interruptions of the train controlling current, butit should'be clearly understood that this limitation is not necessaryand that any reasonable number of codes of different frequencies couldbe'used. i Although I have herein shown and described only one form ofrailway trafiic controlling apparatus embodying my invention,

'it is understood that various changes and modifications may be madetherein within the scope of the appended claims without departin fromthe spirit and scope of my invention.

.IIaving thus described my invention what I claim is:

1. In combination, a source of periodically varying electromotive forcesof constant amplitude but different frequencies, a transformer having aprimary receiving energy from said source and a core substantiallysaturated when the primary is supplied with an electromotive force ofone freand a current consuming device connected with er and requiringfor its operation the amount of power supplied thereto when the primaryof the transformer is receiving an electromotive force of such onefrequency.

2. In combination a transformer, means for supplying the primary of saidtransformer with periodically varying electromotive forces of difierentfrequencies but constant amplitude, and a current consuming deviceconnected with the secondary of said transformer and arranged to beoperated only if the primary of the transformer is supplied with anelectromotive force at a frequency at least as great as that required tosubstantially saturate the transformer core.

3. In combination, a source of direct current, a contact operating attimes at different frequencies, a transformer having a primury connectedwith said source through said contact, the core of said transformerbeing substantially saturatedwhen said contact is operating at onefrequency, and a'eurthe secondary of saidtransform rent consuming deviceconnected with the I secondary of said transformer and arranged to beoperated only when said contact is operating at said one frequency or ata higher frequency.

4. In combination, a source of periodically varying electromotive forcesof constant amplitude but different frequencies, two transformers eachhaving a primary reoeivingencrgy from said source and the cores of saidtransformers being substantially saturated at different frequencies ofthe electromotive forces, and two current consuming devices oneconnected with the secondary of each transformer and each arranged to beenergized only when the frequency of the electromotive force applied tothe associated primary is equal to or above the frequency required tosaturate its core.

5. Railway traflic controlling apparatus comprising a train carriedrelay at times energized intermittently at difierentfrequencies, twotransformers each having a primary supplied with periodically varyingcurrent the frequency of which depends upon the he quency ofenergization of said relay, the cores of said transformers beingsubstantially saturated at difierent frequencies of the current suppliedto the associated primaries, and governing means selectively controlledby said transformers in accordance with the frequency of energization ofsaid relay.

6. Railway trafiic controlling apparatus comprising a train carriedrelay at times onergized intermittently at different frequencies, twotransformers each having a primary supplied with periodically varyingcurrent the frequency of which depends upon the frequency ofenergization of said relay, two other relays one connected with thesecond ary of each said transformer, a rectifier interposed between eachsuch relay and the associated transformer secondary, and governing meansselectively controlled by said other relays in accordance with thefrequency of energization of said train carried relay.

7. In combination, two transformers, means for supplying the primariesof both said transformers with periodically varying electromotive forcesof different frequencies, and two current consuming devices oneconnected with the secondary of each transformer, the transformer coresbeing substantially saturated at different frequencies of theelectromotive forces supplied to the primaries thereof so that thedevices are energized only when the frequencies of saidelectromotiveforces are above different values.

8. Railway traffic controlling apparatus comprising a train carriedrelay at times energized intermittently at different frequencies, twotransformers having different saturation characteristics, meanscontrolled by said relay for creating in said t1 ansformers periodicallyvarying fluxes the frequencies of which vary in accordance with thefrequency of cnergization of said relay, two selector relays oneconnected with the secondary of each transformer, a rectifier interposedbeiween each such selector relay and the associated transformersecondary, and governing means selectively controlled by said selectorrelays in accordance with the frequency of energization of said traincarried relay.

9. In combination, two transformers, means for at times creating in thecores of said transformers periodically varying fluxes of one frequencyand for at other times creating in such cores periodically varyingfluxes of a different frequency, one core being saturated by flux of thefirst frequency and the other core being saturated by flux of the otherfrequency, two current consuming devices one connected with thesecondary of each transformer and each arranged to be energized onlywhen the associated transformer is being supplied with flux at afrequency at least as high as the frequency at which the core of suchtransformer becomes saturated.

10. In combination a first relay at times intermittently energized atdifferent frequencies, two transformers, means controlled by said firstrelay for supplying current to the primaries of said transformers, tworelays one connected with the secondary of each transformer and soarranged that one relay is energized when the frequency of energizationof said first relay is above a predetermined low value and below apredetermined higher value but that both said relays are encrgized whenthe frequency of energization of said first relay is above said highervalue.

1.1. In combination, a stretch of railway track, a contact, means foroperating said contact intermittently at different speeds, and meansincluding said contact for supplying current to the stretch.

12. In combination, a stretch of railway track, a coding relaycomprising a contact arranged to be periodically closed at differentfrequencies, and means controlled by said contact for supplyingalternating current to the rails of said stretch. 13. In combination, astretch of railway track, a contact, a source of alternating current,means including said contact for con necting said source with the railsof the stretch, and means for at times repeatedly opening and closingsaid contact at different speeds.

14- In combination, a stretch of railway track, a coding relaycomprising a contact at times operated intermittently, means for varyingthe speed of operation of said contact, a first source of alternatingcurrent, means including said contact for at times connecting said firstsource with the rails of the stretch, a second source of alternatingcurrent, and means effective only when said first source is disconnectedfrom the rails for connecting said second source with the rails of thestretch.

15. In combination, a stretch of railway track, means including a codingrelay for supplying the rails of the stretch with alternate impulses ofalternating currents of different frequencies, and means for at timesvarying the speed of operation of said coding relay to vary thefrequency of the impulses supplied to the trackway.

16. In combination, a stretch of railway track, a multiple speed codingrelay comprising a movable armature, two windings for moving thearmature in opposite directions, means for supplying current to aselected portion of each winding, .Ineans controlled by said armaturefor alternately shunting such selected portion of said windings, acontact controlled by said armature, and means including said contactfor at times supplying interrupted alternating current to the rails ofthe stretch.

17. Railway traffic controlling apparatus comprising a stretchofrailwaytrack,amultiple speed coding relay comprising a movablearmature, two windings for moving the armature in opposite directions,means for supplying current to a selected portion of each winding, meanscontrolled by said armature for alternately shunting such selectedportion of said windings, a source of alternating eurrcnt, a contactcontrolled by said armature, means including said contact for at timessupplying the rails with alternating current interrupted at differentfrequencies depending upon the operating speed of the relay, andgoverning means on a train selectively responsive to such interruptions.

18. In combination, a stretch of railway track, a relay comprising amovable armature, two windings arranged when energized to move thearmature in opposite directions, means for supplying current to saidwindings, means controlled by the armature for alternately shunting saidwindings, means controlled by said armature for supplying interruptedcurrent to thestretch, and means effective when said stretch isunoccupied to prevent the shunting of one said winding to stop therelay.

19. In combination, a stretch of railway track, a relay comprising amovable armature, two windings arranged when energized to move thearmature in opposite directions, means for supplying current to saidwindings, means controlled by the armature for alternately shunting saidwindings, means controlled by said armature and effective when the relayis operating to supply said stretch with alternate impulses of trackcircuit current and train controlling current, and means effective whenthe stretch is unoccupied to prevent the shunting of one of said windingto stop the relay in such positionthat the quencies, means fortranslating said ,variastretch is supplied continuously with track tionsinto alternating currents of the same circuit current. frequencies asthe variations, and governing 1o 20. Railway traific controllingapparatus means selectively controlled by said last 5 comprising meansfor supplying the tracknamed current.

Way with alternating current having its In testimony whereof I aflix mysignature. amplitude periodically varied atdifi'erent fre- CLARENCE S.SNAVELY.

